drm/i915: Don't set up the LVDS if it isn't in the BIOS device table.

We not only check the device type, but also check the addin_offset. If the
addin_offset is zero, it won't be initialized.
Signed-off-by: NZhao Yakui <yakui.zhao@intel.com>
Reviewed-by: NAdam Jackson <ajax@redhat.com>
Signed-off-by: NEric Anholt <eric@anholt.net>
[anholt: hand-applied due to conflicts]

drivers/gpu/drm/i915/intel_lvds.c

@@ -968,6 +968,46 @@ static void intel_find_lvds_downclock(struct drm_device *dev,
 	return;
 }
 
+/*
+ * Enumerate the child dev array parsed from VBT to check whether
+ * the LVDS is present.
+ * If it is present, return 1.
+ * If it is not present, return false.
+ * If no child dev is parsed from VBT, it assumes that the LVDS is present.
+ * Note: The addin_offset should also be checked for LVDS panel.
+ * Only when it is non-zero, it is assumed that it is present.
+ */
+int lvds_is_present_in_vbt(struct drm_device *dev)
+{
+	struct drm_i915_private *dev_priv = dev->dev_private;
+	struct child_device_config *p_child;
+	int i, ret;
+
+	if (!dev_priv->child_dev_num)
+		return 1;
+
+	ret = 0;
+	for (i = 0; i < dev_priv->child_dev_num; i++) {
+		p_child = dev_priv->child_dev + i;
+		/*
+		 * If the device type is not LFP, continue.
+		 * If the device type is 0x22, it is also regarded as LFP.
+		 */
+		if (p_child->device_type != DEVICE_TYPE_INT_LFP &&
+			p_child->device_type != DEVICE_TYPE_LFP)
+			continue;
+
+		/* The addin_offset should be checked. Only when it is
+		 * non-zero, it is regarded as present.
+		 */
+		if (p_child->addin_offset) {
+			ret = 1;
+			break;
+		}
+	}
+	return ret;
+}
+
 /**
  * intel_lvds_init - setup LVDS connectors on this device
  * @dev: drm device
@@ -991,6 +1031,10 @@ void intel_lvds_init(struct drm_device *dev)
 	if (dmi_check_system(intel_no_lvds))
 		return;
 
+	if (!lvds_is_present_in_vbt(dev)) {
+		DRM_DEBUG_KMS("LVDS is not present in VBT\n");
+		return;
+	}
 	/* Assume that any device without an ACPI LID device also doesn't
 	 * have an integrated LVDS.  We would be better off parsing the BIOS
 	 * to get a reliable indicator, but that code isn't written yet.